The lone-range objectives are to elucidate the immunoregulatory roles of prolactin (PRL), growth hormone (GH), and placental lactogen (PL). The immediate hypothesis we propose to test is that these hormones alter lymphocyte proliferation in Class II restricted immune responses. The specific aims are to determine: (a) Whether these hormones alter the cell surface markers of lymphoid cells by using monoclonal antibodies to the cell surface markers and fluorescent activated cell sorter analyses. (b) Whether these hormones alter the antigenicity of lymphoid cells by using hormone-treated lymphoid cells as stimulators for allogeneic or syngeneic reactions. (c) Whether the lymphoid cells isolated from mice with different circulating levels of the hormones differ in cell surface markers or responsiveness to lymphokines. (d) Whether the hormones affect the antigen presenting activity of monocytes/macrophages. (e) Whether the activities of the hormones differ. Completion of these studies will allow us to identify the hormone responsive cells. The results obtained from the studies would aid in clarifying the immunoregulatory roles of the hormones. Future studies would involve determining the roles of the hormones in development of the immune system and in autoimmune or lymphoproliferative diseases.